System and method for beamformed broadcast and synchronization signals in massive multiple input multiple output communications systems

ABSTRACT

A method for transmitting beamformed signals includes beamforming a synchronization signal in accordance with a first set of spatially separated transmission beams, thereby producing first beamformed synchronization signals, transmitting the first beamformed synchronization signals, determining if a first synchronization cycle is complete, and when the first synchronization cycle is not complete, rotating the first set of spatially separated transmission beams, and repeating the beamforming, the transmitting, and the determining until the first synchronization cycle is complete.

This application claims the benefit of U.S. Provisional Application No.62/367,407, filed on Jul. 27, 2016, entitled “A System and Method forBeamformed Broadcast and Synchronization Signals in Massive MultipleInput Multiple Output Communications Systems,” which application ishereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to a system and method fordigital communications, and, in particular embodiments, to a system andmethod for beamformed broadcast and synchronization signals in massivemultiple input multiple output (MIMO) communications systems.

BACKGROUND

Beamforming is a technique that makes use of antenna arrays fordirectional transmission or reception of signals. The elements of theantenna array are combined in such a way that signals in certaindirections experience constructive interference while those in otherdirections experience destructive interference. Communications beamresult with enhance performance in certain directions. In cellularcommunications systems, beamforming is used to improve the link budgetfor data communications. Examples of cellular communications systemsthat benefit from beamforming are the systems that operate atfrequencies greater than 6 GHz, such as millimeter wave (mmWave)communications systems, as well as massive MIMO communications systems.

However, beamforming is also helpful in improving the link budget forcell specific signals, such as broadcast signals (e.g., physicalbroadcast signals (PBCH)) and synchronization signals (e.g., primarysynchronization signals (PSS) and secondary synchronization signals(SSS)).

SUMMARY

Example embodiments provide a system and method for beamformed broadcastand synchronization signals in massive multiple input multiple output(MIMO) communications systems.

In accordance with an example embodiment, a method for transmittingbeamformed signals is provided. The method includes beamforming, by atransmit-receive point (TRP), a synchronization signal in accordancewith a first set of spatially separated transmission beams, therebyproducing first beamformed synchronization signals, transmitting, by theTRP, the first beamformed synchronization signals, determining, by theTRP, if a first synchronization cycle is complete. When the firstsynchronization cycle is not complete, the method includes rotating, bythe TRP, the first set of spatially separated transmission beams, andrepeating, by the TRP, the beamforming, the transmitting, and thedetermining until the first synchronization cycle is complete.

In accordance with an example embodiment, a method for synchronizing auser equipment (UE) is provided. The method includes determining, by theUE, a first beam identifier associated with a transmission beamconveying a first received beamformed synchronization signal, anddetermining, by the UE, if a first synchronization cycle is complete.When the first synchronization cycle is not complete, the methodincludes repeating, by the UE, the determining the first beamidentifier, and the determining if the first synchronization cycle isnot complete until the first synchronization cycle is complete.

In accordance with an example embodiment, a TRP adapted to transmitbeamformed control signals is provided. The TRP includes a processor,and a computer readable storage medium storing programming for executionby the processor. The programming including instructions to configurethe TRP to beamform a synchronization signal in accordance with a firstset of spatially separated transmission beams, thereby producing firstbeamformed synchronization signals, transmit the first beamformedsynchronization signals, determine if a first synchronization cycle iscomplete, and when the first synchronization cycle is not complete,rotate the first set of spatially separated transmission beams, andrepeat beamforming, transmitting, and determining until the firstsynchronization cycle is complete.

In accordance with an example embodiment, a UE is provided. The UEincludes a processor, and a computer readable storage medium storingprogramming for execution by the processor. The programming includinginstructions to configure the UE to determine a first beam identifierassociated with a transmission beam conveying a first receivedbeamformed synchronization signal, determine if a first synchronizationcycle is complete, and when the first synchronization cycle is notcomplete, repeat determining the first beam identifier, and determiningif the first synchronization cycle is not complete until the firstsynchronization cycle is complete.

Practice of the foregoing embodiments enables the beamforming of cellspecific broadcast signals and synchronization signals with reducedoverhead. The reduced overhead enables synchronization in spatial,frequency, and time domains. The reduced overhead also allows for theproviding of cell identifier information.

Practice of the foregoing embodiments also accommodate transmit-receivepoints (TRPs) with different numbers of radio frequency (RF) chains orability to simultaneously form different numbers of communicationsbeams.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is an example wireless communications system according to exampleembodiments described herein;

FIG. 2A illustrates a communications system highlighting thetransmission of cell specific broadcast signals and synchronizationsignals using narrow beams according to example embodiments describedherein;

FIG. 2B illustrates a communications system highlighting thetransmission of cell specific broadcast signals and synchronizationsignals using an omni directional beam according to example embodimentsdescribed herein;

FIG. 3A illustrates a communications system highlighting thesimultaneous transmission of beamformed broadcast signals using allavailable transmission beams according to example embodiments describedherein;

FIG. 3B illustrates a communications system highlighting thetransmission of beamformed broadcast signals on different frequencysubbands according to example embodiments described herein;

FIG. 3C illustrates a communications system highlighting thetransmission of beamformed broadcast signals with a combination of TXdiversity and subbands according to example embodiments describedherein;

FIG. 4 illustrates a communications system highlighting the simultaneoustransmission of beamformed synchronization signals in a plurality oftransmission beams that are spatially separated according to exampleembodiments described herein;

FIGS. 5A-5E illustrate a first example sequence of beamformed signalstransmitted by a TRP according to example embodiments described herein;

FIGS. 6A-6F illustrate a second example sequence of beamformed signalstransmitted by a TRP according to example embodiments described herein;

FIG. 7 illustrates an example time-frequency plot highlighting thetransmission of beamformed synchronization signals in separate frequencyblocks according to example embodiments described herein;

FIG. 8 illustrates an example time-frequency plot highlighting thetransmission of beamformed synchronization signals in separate frequencyblocks with rotations according to example embodiments described herein;

FIG. 9 illustrates a third example sequence of beamformed transmissionsmade by a TRP according to example embodiments described herein;

FIG. 10 illustrates a fourth example sequence of beamformedtransmissions made by a TRP according to example embodiments describedherein;

FIG. 11 illustrates an example sequence of beamformed synchronizationsignals transmitted by a TRP, where the active beams are spatiallyseparated and have the same beam identity according to exampleembodiments described herein;

FIG. 12 illustrates angular relationship between TRP and UE according toexample embodiments described herein;

FIG. 13 illustrates a fourth example sequence of beamformedtransmissions made by a TRP according to example embodiments describedherein;

FIG. 14 illustrates a fifth example sequence of beamformed transmissionsmade by a TRP according to example embodiments described herein;

FIG. 15 illustrates a diagram of messages exchanged and processingperformed by devices participating in synchronization according toexample embodiments described herein;

FIG. 16 illustrate a diagram of PSS and SSS in current generation 3GPPLTE communications systems according to example embodiments describedherein;

FIG. 17 illustrates a first example beamformed synchronization signalpayload and frame structure for spatial, frequency and timesynchronization according to example embodiments described herein;

FIG. 18 illustrates a second example beamformed synchronization signalpayload and frame structure for spatial, frequency and timesynchronization according to example embodiments described herein;

FIG. 19A illustrates a first example beamformed synchronization signalformat according to example embodiments described herein;

FIG. 19B illustrates a second example beamformed synchronization signalformat according to example embodiments described herein;

FIG. 20A illustrates a flow diagram of first example operationsoccurring in a TRP transmitting beamformed control signals according toexample embodiments described herein;

FIG. 20B illustrates a flow diagram of second example operationsoccurring in a TRP transmitting beamformed control signals according toexample embodiments described herein;

FIG. 21 illustrates a flow diagram of example operations occurring in aUE performing synchronization according to example embodiments describedherein;

FIG. 22 illustrates a block diagram of an embodiment processing systemfor performing methods described herein; and

FIG. 23 illustrates a block diagram of a transceiver adapted to transmitand receive signaling over a telecommunications network according toexample embodiments described herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently example embodiments are discussedin detail below. It should be appreciated, however, that the presentdisclosure provides many applicable inventive concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the embodiments, and do not limit the scope of the disclosure.

FIG. 1 illustrates an example wireless communications system 100.Communications system 100 includes an access node 105 serving aplurality of user equipments (UEs), such as UE 110, UE 112, and UE 114.In a first operating mode, transmissions for UEs as well astransmissions by UEs pass through access node 105. Access node 105allocates network resources for the transmissions to or from the UEs.Access nodes may also be commonly referred to as evolved NodeBs (eNBs),base stations, NodeBs, master eNBs (MeNBs), secondary eNBs (SeNBs),remote radio heads, access points, and the like, while UEs may also becommonly referred to as mobiles, mobile stations, terminals,subscribers, users, stations, and the like. An access node (or an eNB,eNodeB, NodeB, MeNBs, SeNBs, remote radio head, access point,transmission point (TP), transmission and receive point (TRP), basestation, and so on) that is serving one or more UEs may be referred toas a serving base station (SBS). A TP may be used to refer to any devicecapable of transmitting. Therefore, transmission points may refer toaccess nodes, eNBs, base stations, NodeBs, MeNBs, SeNBs, remote radioheads, access points, UEs, mobiles, mobile stations, terminals,subscribers, users, and the like. A TRP refers to a transmission pointthat also is capable of receiving.

While it is understood that communications systems may employ multipleaccess nodes capable of communicating with a number of UEs, only oneaccess node, and 5 UEs are illustrated for simplicity.

A cell is a commonly used term that refers to a coverage area of anaccess node. Typically, a cell is served by one or more sectors of asectorized antenna of the access node. Hence, the coverage area of theaccess node includes a cell partitioned into a plurality of sectors. Asan illustrative example, in a scenario where an access node uses athree-sector antenna system, the cell of the access node may be dividedinto three sectors, with each sector being covered by a separate antenna(with an example beam width of 120 degrees) or a separate part of thetotal antenna system. As another illustrative example, in a scenariowhere an access node uses a six-sector antenna system (where eachantenna may cover a 60 degree sector, for example), the cell of theaccess node may be divided into six sectors or three sectors, with eachsector being covered by one or two antennas or parts sectors of theantenna system respectively.

A technique for providing beamformed cell specific broadcast signals andsynchronization signals involves the transmission of the signals one ata time using narrow beams and then sweeping through availabletransmission beams. FIG. 2A illustrates a communications system 200highlighting the transmission of cell specific broadcast signals andsynchronization signals using narrow beams. Communications system 200includes a transmission-reception point (TRP) 205. TRP 205 istransmitting cell specific broadcast signals and synchronization signalsin narrow beam 210. TRP 205 transmits the signals using narrow beam 210for a period of time and changes to a next narrow beam and transmits thesignals for another period of time. TRP 205 cycles through all of thenarrow beams, transmitting the signals in each narrow beam.

Another technique involves the transmission of the signals using widerbeams with repetition coding. FIG. 2B illustrates a communicationssystem 250 highlighting the transmission of cell specific broadcastsignals and synchronization signals using an omni directional beam.Communications system includes a TRP 255. TRP 255 is transmitting cellspecific broadcast signals and synchronization signals in omnidirectional beam 260. Repetition coding (in the time, frequency, or codedomain) is used to improve reception performance. Although FIG. 2Billustrates the use of an omni directional beam, smaller beams (referredto as semi-omni directional beams) that are wider than narrow beams maybe used. If semi-omni directional beams are used, the TRP cycles througha plurality of semi-omni directional beams to provide full coverage. Theuse of omni directional or semi-omni directional beams reduce the numberof beams the TRP has to use to transmit the signals. In a situationwhere the environment is changing with time or if the communicationssystem has high phase noise (which generally drifts with time), the useof narrow beams may yield better performance than omni beams.

A technique used to transmit beamformed broadcast signals, such asphysical broadcast channel (PBCH) signals, involves the simultaneoustransmission of beamformed broadcast signals using all availabletransmission beams. A transmit (TX) diversity technique, such as cyclicdelay diversity (CDD), is used for the transmission, so that, the sameinformation transmitted on the different beams do not interfere witheach other. This technique reduces the overhead (in terms of time,frequency, and code resources) involved in the transmission of thebroadcast signals at the TRP, while the UEs inherently reap the benefitsof TX diversity. FIG. 3A illustrates a communications system 300highlighting the simultaneous transmission of beamformed broadcastsignals using all available transmission beams. Communications system300 includes a TRP 305. TRP 305 simultaneously transmits beamformedbroadcast signals on all available transmission beams, such astransmission beam 310, transmission beam 312, and transmission beam 314.As shown in FIG. 3A, TRP 305 has a complement of 16 transmission beams.Different TRPs may have different numbers of transmission beams.

In order to utilize TX diversity, each transmission beam has to transmitthe same data. Therefore, any beam index information usable insubsequent connection processes is lost. However, loss of beam indexinformation is not an issue in broadcast signals. The TRP has to be ableto beamform (or has a sufficient number of RF chains) and transmit thebroadcast signals in all of the transmission beams at the same time.Furthermore, due to practical or regulatory restrictions on the maximumTX power (power spectral density, per antenna port, overall spatial TXpower, and so on) it may be necessary to reduce the TX power pertransmission beam if all beams are used simultaneously and in the samefrequency.

Another technique used to transmit beamformed broadcast signals involvesthe transmission of beamformed broadcast signals on different frequencysubbands. FIG. 3B illustrates a communications system 330 highlightingthe transmission of beamformed broadcast signals on different frequencysubbands. Communications system 330 includes a TRP 335. TRP 335transmits beamformed broadcast signals on different frequency subbandswith different transmission beams on different subbands. As an example,a first transmission beam 340 is transmitted on subband F1, a secondtransmission beam 342 is transmitted on subband F2, a third transmissionbeam 344 is transmitted on subband F3, and so on. Each transmission beamis used in a different subband. The use of different subbands for eachtransmission beam may alleviate the restriction on maximum TX power(depending on how the maximum power is defined). However, this techniqueis supported only when digital or hybrid beamforming is used.

Yet another technique used to transmit beamformed broadcast signalsinvolves the multiplexing of the beamformed broadcast signals with acombination of TX diversity and subbands. FIG. 3C illustrates acommunications system 350 highlighting the transmission of beamformedbroadcast signals with a combination of TX diversity and subbands.Communications system 350 includes a TRP 355. TRP 355 transmits thebeamformed broadcast signals in subsets of available transmission beamswith each subset being transmitted in different subbands. As an example,a first subset of transmission beams 360 (including transmission beams362 and 364) are used to transmit beamformed broadcast signals in afirst subband (subband 1), a second subset of transmission beams 366(including transmission beams 368 and 370) are used to transmitbeamformed broadcast signals in a second subband (subband 2), and so on.

According to an example embodiment, cell specific beamformed broadcastchannels are transmitted with TX diversity on two or more adjacenttransmission beams. The number of adjacent transmission beams may be anynumber between 2 and a maximum number of transmission beams that a TRPcan simultaneously form and transmit. Any form of TX diversity can beused, including CDD.

An additional technique used to transmit beamformed broadcast signalsinvolves the transmission of a subset of the beamformed broadcastsignals after a corresponding set of beamformed synchronization signalsare transmitted. TX diversity and/or subbands may be used.

In order to facilitate synchronization of the UE with the TRP (where theUE obtains timing information and an initial preferred beam indexdirection from the TRP), as well as reception of beamformed broadcastsignals, a technique is needed with reduced sounding overhead. In somedeployments, such as in a heterogeneous deployment with low power mmWaveTRPs operating in the coverage area of legacy cells, each TRP may not berequired to broadcast control channel information. This is because thebroadcast control channel information for the respective TRPs andneighbor TRPs may be provided by the legacy cells.

In a traditional cellular communications system, a high-level procedurewhere a UE connects with an access node is as follows:

1) The UE obtains downlink synchronization with the access node (usingsynchronization signals, such as PSS and SSS);

2) The UE demodulates a downlink broadcast channel (e.g., PBCH)transmitted by the access node;

3) The UE initiates a random access procedure by transmitting a randomaccess channel (RACH) signal (e.g., a RACH preamble); If successful, theaccess node transmits a random access response (RAR) and the access nodeallocates time and frequency resources to the UE; and

4) The UE demodulates downlink data using assigned downlink controlinformation (DCI) and reference signals.

In a cellular communications system that uses beamformed control andreference signals, a high-level procedure where a UE connects with anaccess node is as follows:

a) The UE obtains downlink synchronization with the access node (usingbeamformed synchronization signals, such as beamformed PSS and SSS);

b) The UE demodulates a downlink beamformed broadcast channel (e.g.,beamformed PBCH) transmitted by the access node;

c) The UE initiates a random access procedure by transmitting a RACHsignal, e.g., a RACH preamble, (which is received with beamforming bythe access node); If successful, the access node transmits a RAR and theaccess node allocates time and frequency resources to the UE;

d) The access node establishes best beam directions for the UE by usingfeedback corresponding to beamformed channel state information referencesignals (CSI-RS) or from sounding reference signals (SRS); and

e) The UE demodulates beamformed downlink data using associatedbeamformed control reference signals.

In communications systems where the signals can easily be blocked byobjects (e.g., hands, people, walls, etc.) near the UE, such as mmWavecommunications systems, the UE may also transmit the RACH signal, e.g.,a RACH preamble, using beamforming.

According to an example embodiment, systems and methods for thetransmission and reception of cell specific beamformed broadcast andsynchronization signals are provided. These systems and methods incurless overhead than existing techniques; therefore, improved performanceis realized.

According to an example embodiment, beamformed synchronization signalsare simultaneously transmitted on a plurality of spatially separatedtransmission beams. The transmission beams transmitted together haveunique identifiers. The transmission beams are rotated with time, andtheir identifiers change as the transmission beams are rotated. Therotations occur each symbol time, time slot, or subframe. Deploymentswhere interference between transmission beams (or expected reflectionsfrom different transmission beams) is low are good candidates for thisexample embodiment. Examples of such deployments are communicationssystems operating in the 60 GHz to 90 GHz range. However, this exampleembodiment may be used with communications systems operating in otherfrequency ranges and furthermore, for communications systems wherein theactive transmission beams (and/or the sequence or code identifying thedifferent beams) have low cross correlation.

According to an example embodiment, beamformed synchronization signalsare simultaneously transmitted by a TRP on a plurality of transmissionbeams (the active transmission beams) that are spatially separated. Eachactive transmission beam has a different identifier and is rotated intime. The spatial separation between the transmission beams ismaintained between rotations. The plurality of transmission beams is asubset of all transmission beams available at the TRP. The transmissionbeams in the plurality of transmission beams, as well as the spatialseparation between the transmission beams, may be dependent upon thecapabilities and configuration of the communications system.

FIG. 4 illustrates a communications system 400 highlighting thesimultaneous transmission of beamformed synchronization signals in aplurality of transmission beams that are spatially separated.Communications system 400 includes a TRP 405. For discussion purposes,consider a situation where TRP 405 has a total of 16 transmission beams,each being 20 degrees wide. As shown in FIG. 4, TRP 405 transmitsbeamformed synchronization signals in 4 transmission beams (transmissionbeams 410-416) with each transmission beam being spatially separated by90 degrees. The transmission in the 4 transmission beams occurs for aspecified time interval. It is noted that if TRP 405 is capable ofbeamforming and transmitting more than 4 beams, then the plurality oftransmission beams may include more than 4 beams. Similarly, if TRP 405is incapable of beamforming and transmitting 4 beams, then the pluralityof transmission beams includes less than 4 beams (e.g., 2 or 3 beams).Therefore, the discussion of 4 transmission beams should not beconstrued as being limiting to either the scope or the spirit of theexample embodiments.

Each transmission beam has a unique identifier, e.g., transmission beam410 has identifier ID 1, transmission beam 412 has identifier ID 5,transmission beam 414 has identifier ID 9, and transmission beam 416 hasidentifier ID 13. The identifier of a transmission beam may bedetermined by a sequence used in generating the transmission occurringon the transmission beam. After transmitting in the transmission beams410-416 for the specified amount of time, TRP 405 stops transmitting inthe transmission beams 410-416 and rotates to a new plurality of beams.The new plurality of beams has the same number of beams (e.g., 4 beams)and the same spatial separation. However, the transmission beams in thenew plurality of beams have different identifiers.

Table 1 illustrates example identifiers of transmission beams for thedifferent rotation numbers for a TRP with a total of 16 transmissionbeams and 4 active transmission beams at any given time. The beamidentifiers are conveyed via the code or sequence transmitted by eachtransmission beam. The plurality of beams used in transmitting thebeamformed synchronization signals may be coordinated with neighboringTRPs. Systems and methods for coordinating the plurality of beams usedto transmit the beamformed synchronization signals are presented indetailed in co-assigned U.S. patent application Ser. No. 14/815,571,entitled “System and Method for Beam-Formed Reference/Control Signals,”filed Jul. 31, 2015, which is hereby incorporated herein by reference.

TABLE 1 Transmission beam identifiers for different rotations. TimeFirst Second Third Fourth (Rotation #) Beam ID Beam ID Beam ID Beam IDT1 ID 1 ID 5 ID 9 ID 13 T2 ID 2 ID 6 ID 10 ID 14 T3 ID 3 ID 7 ID 11 ID15 T4 ID 4 ID 8 ID 12 ID 16

As discussed previously, it may be advantageous to transmit thebeamformed broadcast signals using TX diversity. FIGS. 5A-5E illustratea first example sequence of beamformed signals transmitted by a TRP.FIG. 5A illustrates a diagram 500 of simultaneously transmittedbeamformed synchronization signals made by TRP 505 at a first timeinterval. As shown in FIG. 5A, at the first time interval, TRP 505simultaneously transmits 4 beamformed synchronization signals on 4transmission beams that are spatially separated by 90 degrees. A firsttransmission beam 507 transmits a beamformed synchronization signal withidentifier ID 1, a second transmission beam 509 transmits a beamformedsynchronization signal with identifier ID 5, a third transmission beam511 transmits a beamformed synchronization signal with identifier ID 9,and a fourth transmission beam 513 transmits a beamformedsynchronization signal with identifier ID 13. The arrangement oftransmission beams that are used to simultaneously transmit beamformedsynchronization signals is referred to as a set of spatially separatedtransmission beams. FIG. 5B illustrates a diagram 520 of simultaneouslytransmitted beamformed synchronization signals made by TRP 505 at asecond time interval. As shown in FIG. 5B, at the second time interval,TRP 505 simultaneously transmits 4 beamformed synchronization signals on4 transmission beams that are spatially separated by 90 degrees, howeverthe 4 transmission beams are rotated by one beam width. In addition tothe rotation, the identifiers of the beamformed synchronization signalsare also changed.

FIG. 5C illustrates a diagram 530 of simultaneously transmittedbeamformed synchronization signals made by TRP 505 at a third timeinterval. As shown in FIG. 5C, at the third time interval, TRP 505simultaneously transmits 4 beamformed synchronization signals on 4transmission beams that are spatially separated by 90 degrees with the 4transmission beams being rotated by another beam. In addition to therotation, the identifiers of the beamformed synchronization signals arealso changed. FIG. 5D illustrates a diagram 540 of simultaneouslytransmitted beamformed synchronization signals made by TRP 505 at afourth time interval. As shown in FIG. 5D, at the fourth time interval,TRP 505 simultaneously transmits 4 beamformed synchronization signals on4 transmission beams that are spatially separated by 90 degrees with the4 transmission beams being rotated by yet another beam. In addition tothe rotation, the identifiers of the beamformed synchronization signalsare also changed. It is noted that the same set of spatially separatedtransmission beams is used in all four time intervals, only differing inidentifiers and by rotation. The transmission of the beamformedsynchronization signals in four rotations as shown in FIGS. 5A-5Dencompasses the full coverage area of TRP 505 and uses all availabletransmission beams. In other words, after four rotations as shown inFIGS. 5A-5D, TRP 505 has transmitted beamformed synchronization signalsusing all available transmission beams. If different numbers oftransmission beams are available or if a different configuration oftransmission beams are used per rotation, then different number ofrotations may be needed to fully encompass the full coverage area of TRP505. Furthermore, each rotation shown in FIGS. 5A-5D involves a rotationamount equal to 1 beam width. Other values for rotation amounts arepossible, such as 2 beams, 3 beams, and so forth.

FIG. 5E illustrates a diagram 550 of simultaneously transmittedbeamformed broadcast signals made by TRP 505. As shown in FIG. 5E, TRP505 simultaneously transmits beamformed broadcast signals on allavailable transmission beams with TX diversity to fully encompass thecoverage area of TRP 505. Any of the previously described techniques fortransmitting beamformed broadcast signals, such as using differentsubbands, or a combination of different subbands and TX diversity, etc.,may be used. The four transmissions shown in FIGS. 5A-5D make up asynchronization cycle, and the four transmissions shown in FIGS. 5A-5Dwith the transmission shown in FIG. 5E is referred to as a synchronizingcycle and/or frame structure.

It is noted that although the beamformed broadcast signals are shown inFIG. 5E as being transmitted by TRP 505, in alternative deployments, adifferent device may be responsible for providing the broadcastinformation. As an illustrative example, in a heterogeneous deployment,a small cell TRP transmits the beamformed synchronization signals, whilea legacy eNB transmits the broadcast signal.

The number of broadcast signals would generally be fixed by the operatorof the communications system or technical standard. Depending upon thedetected beam identifier, a UE would know the time offset in order toreceive the beamformed broadcast signal from the TRP. The configurationshown in FIGS. 5A-5E may be expressed in simplified notation as

-   -   {SCH(1st rotation), SCH(2nd rotation), SCH(3rd rotation),        SCH(4th rotation), PBCH(all)},        Where: SCH beamformed synchronization channels; and

PBCH beamformed broadcast channels.

The sequence of rotations and the relationship between the transmissionsof the beamformed synchronization signals and the beamformed broadcastsignals illustrated in FIGS. 5A-5E are for illustrative purposes only.Other orderings of the rotations or arrangements of the set of spatiallyseparated transmission beams, as well as the order of beamformedsynchronization signals and beamformed broadcast signals are possible.The illustrated set of spatially separated transmission beams,rotations, and relationships should not be construed as being limitingto either the scope or spirit of the example embodiments.

However, some TRPs may not be capable of simultaneously transmitting thebeamformed broadcast signals on all transmission beams. According to anexample embodiment, in a situation where a TRP is incapable ofsimultaneously transmitting beamformed broadcast signals on alltransmission beams, the TRP may transmit the beamformed broadcastsignals on a subset of all transmission beams and rotate the beams in amanner similar to the rotation of the beams discussed in thetransmission of the beamformed synchronization signals.

FIGS. 6A-6F illustrate a second example sequence of beamformed signalstransmitted by a TRP. FIG. 6A illustrates a diagram 600 ofsimultaneously transmitted beamformed synchronization signals made byTRP 605 at a first time interval. As shown in FIG. 6A, TRP 605simultaneously transmits 4 beamformed synchronization signals on a setof spatially separated transmission beams comprising 4 transmissionbeams that are spatially separated by 90 degrees in a manner similar towhat is shown in FIG. 5A. FIG. 6B illustrates a diagram 610 ofsimultaneously transmitted beamformed synchronization signals made byTRP 605 at a second time. As shown in FIG. 6B, at the second time, TRP605 simultaneously transmits 4 beamformed synchronization signals on 4transmission beams that are spatially separated by 90 degrees, howeverthe 4 transmission beams are rotated by one beam width. In addition tothe rotation, the identifiers of the beamformed synchronization signalsare also changed.

FIG. 6C illustrates a diagram 620 of simultaneously transmittedbeamformed broadcast signals made by TRP 605 in a third time interval.Due to limitations of TRP 605, TRP 605 can only simultaneously beamformand transmit beamformed broadcast signals on 8 transmission beams, forexample. As shown in FIG. 6C, a set of transmission beams includes 4groups of 2 adjacent transmission beams with a 90 degree spatialseparation between each group. The set of transmission beams used by TRP605 to transmit the beamformed broadcast signals include the sametransmission beams used by TRP 605 to transmit the beamformedsynchronization signals in time intervals 1 (FIG. 6A) and 2 (FIG. 6B).As an example, a group of transmission beams comprises transmissionbeams 625 and 627. TRP 605 may use TX diversity and/or differentsubbands in the transmission of the beamformed broadcast signals. Thethree transmissions shown in FIGS. 6A-6C make up a first synchronizingcycle or frame structure, while the two transmissions shown in FIGS. 6Aand 6B make up a first synchronization cycle.

FIG. 6D illustrates a diagram 640 of simultaneously transmittedbeamformed synchronization signals made by TRP 605 at a fourth timeinterval. As shown in FIG. 6D, at the fourth time interval, TRP 605simultaneously transmits 4 beamformed synchronization signals on 4transmission beams that are spatially separated by 90 degrees, howeverthe 4 transmission beams are rotated by an additional beam width. Inaddition to the rotation, the identifiers of the beamformedsynchronization signals are also changed. FIG. 6E illustrates a diagram650 of simultaneously transmitted beamformed synchronization signalsmade by TRP 605 at a fifth time interval. As shown in FIG. 6E, at thefifth time interval, TRP 605 simultaneously transmits 4 beamformedsynchronization signals on 4 transmission beams that are spatiallyseparated by 90 degrees, however the 4 transmission beams are rotated byanother beam width. In addition to the rotation, the identifiers of thebeamformed synchronization signals are also changed.

FIG. 6F illustrates a diagram 660 of simultaneously transmittedbeamformed broadcast signals made by TRP 605 in a sixth time interval.The set of transmission beams used to transmit the beamformed broadcastsignals as shown in FIG. 6F is similar to the set of transmission beamsshown in FIG. 6C with exception of a rotation being applied to the setof transmission beams. The set of transmission beams used by TRP 605 totransmit the beamformed broadcast signals include the same transmissionbeams used by TRP 605 to transmit the beamformed synchronization signalsin time intervals 4 (FIG. 6D) and 5 (FIG. 6E). As shown in FIG. 6F,transmission beams 665 and 667 correspond to transmission beams 625 and627 shown in FIG. 6C. With the particular configuration of transmissionbeams illustrated in FIGS. 6C and 6F, the rotation is equal to 2 beamwidths. The amount of rotation differs based on the total number oftransmission beams, the number of transmission beams per group, and thenumber of sets of transmission beams. The three transmissions shown inFIGS. 6D-6F make up a second synchronizing cycle or frame structure,while the two transmissions shown in FIGS. 6D and 6E make up a secondsynchronization cycle. The six transmissions shown in FIGS. 6A-6F makeup a complete synchronizing cycle or frame structure.

It is noted that although the beamformed broadcast signals are shown inFIGS. 6C and 6F as being transmitted by TRP 605, in alternativedeployments, a different device may be responsible for providing thebroadcast information. As an illustrative example, in a heterogeneousdeployment, a small cell TRP transmits the beamformed synchronizationsignals, while a legacy eNB transmits the broadcast signals.

The number of beamformed synchronization signals and the number ofbeamformed synchronization signals to beamformed broadcast signals wouldgenerally be fixed by the operator of the communications system ortechnical standard. Then, depending upon the detected beam identifier, aUE would know the time offset to receive the beamformed broadcastsignals. The configuration shown in FIGS. 6A-6F may be expressed insimplified notation as

-   -   {SCH(1st rotation), SCH(2nd rotation), PBCH(1st+2nd rotations),        SCH(3rd rotation), SCH(4th rotation), PBCH(3rd+4th rotations)},        Where: SCH beamformed synchronization channels; and

PBCH beamformed broadcast channels.

The sequence of rotations and the relationship between the transmissionsof the beamformed synchronization signals and the beamformed broadcastsignals illustrated in FIGS. 6A-6F are for illustrative purposes only.Other orderings of the rotations, as well as the order of beamformedsynchronization signals and beamformed broadcast signals are possible.The illustrated rotations and relationships should not be construed asbeing limiting to either the scope or spirit of the example embodiments.

The example embodiments presented herein enable a reduction incommunications overhead by reducing the number of time intervals thebeamformed broadcast signals are transmitted. If the beamformedbroadcast signals are transmitted every time after the transmission ofthe beamformed synchronization signals, the resulting overhead would begreater.

In a Third Generation Partnership Project (3GPP) Long Term Evolution(LTE) compliant communications system, synchronization signals (i.e.,PSS and SSS) occupy 6 resource blocks (RBs) in the frequency domain with62 active and 10 guard subcarriers (SCs). Therefore, even the UEs withthe lowest RB allocations have access to the synchronization signals. Infuture new radio (NR) or mmWave communications systems for 3GPP, theminimum bandwidth allocation may be different, so the number ofsubcarriers for the synchronization signals may also change.

According to an example embodiment, beamformed synchronization signalsthat are transmitted using wideband RF beamforming are transmitted inseparate blocks in the frequency domain. When the beamformedsynchronization signals are transmitted in separate blocks in thefrequency domain, even the UEs that only have the minimum bandwidthallocation can acquire the beamformed synchronization signals at thesame rate as the UEs that have greater bandwidth allocation. However,the UEs with greater bandwidth allocations still have the advantage oflower signal to noise ratio (SNR) due to frequency diversity arisingfrom their greater bandwidth allocation.

FIG. 7 illustrates an example time-frequency plot 700 highlighting thetransmission of beamformed synchronization signals in separate frequencyblocks. As shown in FIG. 7, beamformed synchronization signals aretransmitted in separate frequency blocks, such as frequency blocks 705,707, 709, and 711. In order to simplify operations, the sametransmission beams may be used to transmit the beamformedsynchronization signals in the different frequency blocks at the sametime interval.

When digital (or hybrid) beamforming is used at a TRP for transmittingbeamformed synchronization signals in separate frequency blocks, it maybe possible for the TRP to transmit differently rotated beamformedsynchronization signals in the frequency domain. The number of frequencyblocks in the frequency domain used to transmit the beamformedsynchronization signals may need to be limited so that even the mostbasic UE receiver with the lowest allocated bandwidth is able to derivebenefits of the beamformed synchronization signals.

According to an example embodiment, when transmitting beamformedsynchronization signals, rotations in the time domain and frequencymultiplexing are used to reduce synchronization overhead. It is notedthat UEs with limited bandwidth allocations can still utilize such asystem when the rotations in the frequency domain cover a limited numberof subbands. The application of rotations in the time domain andfrequency multiplexing enables TRPs with neighboring transmission beamswith potential cross-interference issues to transmit the beamformedsynchronization signals at the same time but in different subbands toavoid interference. Additionally, because the different subbands areorthogonal, the number of orthogonal sequences needed is reduced by afactor of N, where N is the number of subbands.

FIG. 8 illustrates an example time-frequency plot 800 highlighting thetransmission of beamformed synchronization signals in separate frequencyblocks with rotations. As shown in FIG. 8, frequency blocks, such asfrequency blocks 805 and 807, occurring at the first time are used totransmit beamformed synchronization signals with different sets oftransmission beams. As shown in FIG. 8, set of transmission beams 806 isused in frequency block 805 and set of transmission beams 808 is used infrequency block 807. Furthermore, at a second time, frequency blocks 810and 812 are used to transmit synchronization signals with sets oftransmission beams 811 and 813, respectively. It is noted that the setsof transmission beams may have the same base set of transmission beams,but with different rotations.

FIG. 9 illustrates a third example sequence of beamformed transmissions900 made by a TRP 905. TRP 905 is transmitting beamformed signals indifferent frequency blocks with rotations applied at different times. Ata first time (time_1) 910, TRP 905 transmits beamformed synchronizationsignals using a total of 8 transmission beams, with a first set of 4spatially separated transmission beams (unshaded beams) transmitted in afirst subband and a second set of 4 spatially separated transmissionbeams (crosshatched beams) transmitted in a second subband. Eachtransmission beam has a different beam identity. At a second time(time_2) 915, TRP 905 transmits beamformed synchronization signals usinga total of 8 transmission beams, with a first set of 4 spatiallyseparated transmission beams transmitted in a first subband and a secondset of 4 spatially separated transmission beams transmitted in a secondsubband. The sets of 4 spatially separated transmission beams used insecond time 915 are rotated versions of the sets of 4 spatiallyseparated transmission beams used in first time 910. Each transmissionbeam has a different beam identity. At a third time (time_3) 920, TRP905 transmits beamformed broadcast signals using a total of 16transmission beams, which includes all of the transmission beams used totransmit the beamformed synchronization signals in first time 910 andsecond time 915. Any of the previously described techniques fortransmitting beamformed broadcast signals, such as using TX diversity,different subbands, or a combination of different subbands and TXdiversity, etc., may be used.

FIG. 10 illustrates a fourth example sequence of beamformedtransmissions made by a TRP 1005. TRP 1005 is transmitting beamformedsignals in different frequency blocks with rotations. At a first time(time_1) 1010, TRP 1005 transmits beamformed synchronization signalsusing a total of 8 transmission beams, with a first set of 4 spatiallyseparated transmission beams (unshaded beams) transmitted in a firstsubband and a second set of 4 spatially separated transmission beams(crosshatched beams) transmitted in a second subband. Each transmissionbeam has a different beam identity. At a second time (time_2) 1015, TRP1005 transmits beamformed broadcast signals using 8 transmission beams,the same 8 transmission beams used in first time 1010. Any of thepreviously described techniques for transmitting beamformed broadcastsignals, such as using TX diversity, different subbands, or acombination of different subbands and TX diversity, etc., may be used.At a third time (time_3) 1020, TRP 1005 beamformed synchronizationsignals using a total of 8 transmission beams, with a first set of 4spatially separated transmission beams transmitted in a first subbandand a second set of 4 spatially separated transmission beams transmittedin a second subband. The sets of 4 spatially separated transmissionbeams used in third time 1020 are rotated versions of the sets of 4spatially separated transmission beams used in first time 1010. At afourth time (time_4) 1025, TRP 1005 transmits beamformed broadcastsignals using 8 transmission beams, the same 8 transmission beams usedin third time 1020. Any of the previously described techniques fortransmitting beamformed broadcast signals, such as using TX diversity,different subbands, or a combination of different subbands and TXdiversity, etc., may be used.

Through the use of 2 subbands, the number of sequences required isreduced from 16 down to 8 in order to ensure that the UE is able toidentify the beam identifiers of the transmission beams. Furthermore,the number of time intervals for transmitting the beamformedsynchronization signals can be reduced from 4 down to 2.

According to an example embodiment, beamformed synchronization signalsare simultaneously transmitted on a plurality of spatially separatedtransmission beams, with unique angular spacing between neighboringactive transmission beams. The transmission beams transmitted togetherhave the same identifier. The transmission beams are rotated in timewith each rotation having a different identifier. The unique angularspacing between active transmission beams eliminates ambiguity.Communications systems that use wider beams and/or communicationssystems that operate in an environment when there are higher incidentsof multiple reflections are good candidates for this example embodiment.

According to an example embodiment, the beamformed synchronizationsignals are simultaneously transmitted on a set of spatially separatedtransmission beams, where all of the transmission beams have the samebeam identity. The transmission beams in the set of spatially separatedtransmission beams are referred to as active beams. TX diversity may beused. The angular spacing between the active beams is different in theangular coverage area. The angular coverage area may be a sector (suchas 120 degrees) or 360 degrees. The active beams rotate with time, andin each rotation the active beams have a different beam identifier. Theangular spacings between the active beams are maintained betweenrotations, and are used to help eliminate ambiguity.

FIG. 11 illustrates an example sequence of beamformed synchronizationsignals transmitted by a TRP 1105, where the active beams are spatiallyseparated and have the same beam identity. As shown in FIG. 11, a totalof 9 rotations of the active beams is needed to provide full coverage,compared to 16 rotations if a single transmission beam was rotated. In afirst time, TRP 1105 transmits the active beams as configured by firstsynchronization signals configuration (SCH_1) 1110. Firstsynchronization signals configuration 1110 includes 3 transmission beams(labeled beams A, B, and C). As shown in FIG. 11, the spatial separationbetween beams A and B is X (e.g., 3 beams), the spatial spacing betweenbeams B and C is Y (e.g., 5 beams), and the spatial separation betweenbeams C and A is Z (e.g., 7 beams). In a second time, TRP 1105 transmitsthe active beams as configured by second synchronization signalsconfiguration (SCH_2) 1115. Second synchronization signals configuration1115 is a rotation of first synchronization signals configuration 1110by an angular amount, e.g., a beam width. In a third time, TRP 1105transmits the active beams as configured by third synchronizationsignals configuration (SCH_3) 1120. In a fourth time, TRP 1105 transmitsthe active beams as configured by fourth synchronization signalsconfiguration (SCH_4) 1125. In a fifth time, TRP 1105 transmits theactive beams as configured by fifth synchronization signalsconfiguration (SCH_5) 1130. In a sixth time, TRP 1105 transmits theactive beams as configured by sixth synchronization signalsconfiguration (SCH_6) 1135. In a seventh time, TRP 1105 transmits theactive beams as configured by seventh synchronization signalsconfiguration (SCH_7) 1140. In an eighth time, TRP 1105 transmits theactive beams as configured by eighth synchronization signalsconfiguration (SCH_8) 1145. In a ninth time, TRP 1105 transmits theactive beams as configured by ninth synchronization signalsconfiguration (SCH_9) 1150.

It is noted that the active beams, the synchronization signalconfigurations, and the rotations illustrated in FIG. 11 are examplesprovided for discussion and are not intended to limit the scope or thespirit of the example embodiments. Alternate configurations of activebeams, synchronization signal configurations, and rotations are possibleas long as the total angular space (360 degrees in this example) isswept and that angular locations that are beamformed at the same time(i.e., transmission beams A, B, and C) have a unique spatial separationand transmit the same beam identifiers (beam identifying sequences, forexample) to eliminate ambiguity. Each rotation of the beams in the timesequence transmits a different beam identifiers. Table 2 displays a setof beam identifiers that are detectable by UEs that are located in thecoverage area of TRP 1105. The UE location in degrees is the anglerelative to TRP, as shown in FIG. 12, which illustrates the relativeangle between UE 1205 and TRP 1105. It is noted that at each position inthe coverage area of TRP 1105, a UE detects a unique set of beamidentities. Therefore, the UE is able to determine an orientation withrespect to TRP 1105 and a beam index.

TABLE 2 Beam identifiers that are detectable by UEs that are located inthe coverage area of a TRP. UE Location (degrees) Beam Identifier 0 ID1 + ID 9 22.5 ID 2 45 ID 3 67.5 ID 4 90 ID 2 + ID 5 112.5 ID 3 + ID 6135 ID 4 + ID 7 157.5 ID 5 + ID 8 180 ID 1 + ID 6 + ID 9 202.5 ID 2 + ID7 225 ID 3 + ID 8 247.5 ID 4 + ID 9 270 ID 5 292.5 ID 6 315 ID 7 337.5ID 8

FIG. 13 illustrates a fourth example sequence of beamformedtransmissions made by a TRP 1305. TRP 1305 is transmitting beamformedsignals using a set of spatially separated transmission beams (i.e.,active beams) with rotations applied at different time intervals. Allactive beams have the same beam identity in a single time interval. At afirst time (time_1) 1310, TRP 1305 transmits beamformed synchronizationsignals using 3 active beams with beam identity 1. At a second time(time_2) 1315, TRP 1305 transmits beamformed synchronization signalsusing 3 active beams with beam identity 2. At a third time (time_3)1320, TRP 1305 transmits beamformed synchronization signals using 3active beams with beam identity 3. At a fourth time (time_4) 1325, TRP1305 transmits beamformed synchronization signals using 3 active beamswith beam identity 4. At a fifth time (time_5) 1330, TRP 1305 transmitsbeamformed synchronization signals using 3 active beams with beamidentity 5. At a sixth time (time_6) 1335, TRP 1305 transmits beamformedsynchronization signals using 3 active beams with beam identity 6. At aseventh time (time_7) 1340, TRP 1305 transmits beamformedsynchronization signals using 3 active beams with beam identity 7. At aneighth time (time_8) 1345, TRP 1305 transmits beamformed synchronizationsignals using 3 active beams with beam identity 8. At a ninth time(time_9) 1350, TRP 1305 transmits beamformed synchronization signalsusing 3 active beams with beam identity 9. At a tenth time (time_10)1355, TRP 1305 transmits beamformed broadcast signals using allavailable transmission beams. Any of the previously described techniquesfor transmitting beamformed broadcast signals, such as using TXdiversity, different subbands, or a combination of different subbandsand TX diversity, etc., may be used. If a TRP is not capable ofsimultaneously transmitting the beamformed broadcast signals on alltransmission beams, the beamformed broadcast signals may be transmittedin different subsets of all transmission beams in different subframes.

When a UE detects a beamformed synchronization signal (and synchronizesits receiver), the UE will know the timing offset to receive anddemodulate the beamformed broadcast signals because the frame structureis fixed. Due to the nature of this example embodiment, all timeinstances of the beamformed synchronization signals (e.g., subframes)will be received before the UE can unambiguously determine which beamdirection from the TRP is the best direction. Once the UE has detectedat least one beam identity with the correct timing, the UE may need tocontinue detecting to the subsequent sets of beamformed synchronizationsignals in order to fully establish the correct beam from the TRP.

According to an example embodiment, the beamformed synchronizationsignals are transmitted in multiple subbands with the same transmissionbeam directions to support frequency diversity or with differenttransmission beam directions to reduce overhead in the time dimension.As discussed previously, when the different beamformed synchronizationsignals are transmitted in different subbands with differenttransmission beam directions, different beam identifiers are used.

FIG. 14 illustrates a fifth example sequence of beamformed transmissionsmade by a TRP 1405. TRP 1405 is transmitting beamformed signals using aset of spatially separated transmission beams (i.e., active beams) indifferent frequency subbands with rotations applied at different timeswith the number of subbands equal to 3. All active beams within a singlefrequency subband in a single time have the same beam identity, but thebeam identities change in different time intervals, even for the sameactive beams within the single frequency subband. In a first subband1410 and at a first time, TRP 1405 transmits beamformed synchronizationsignals using active beams with beam identifier 1 (shown as white beamsin combined first transmissions 1411), at the same time and in a secondsubband TRP 1405 transmits beamformed synchronization signals using theactive beams using a first rotation with beam identifier 2 (shown ashatched beams in combined first transmissions 1411), and at a thirdsubband TRP 1405 transmits beamformed synchronization signals usingactive beams after a second rotation with beam identifier 3 (shown ascross hatched beams in combined first transmissions 1411). In a secondtime and in a the first subband, TRP 1405 transmits beamformedsynchronization signals using active beams with beam identifier 4 (shownas white beams in combined second transmissions 1412), and at the sametime TRP 1405 transmits beamformed synchronization signals using theactive beams after the first rotation with beam identifier 5 (shown ashatched beams in combined second transmissions 1412), and at the sametime TRP 1405 transmits beamformed synchronization signals using activebeams using a further rotation with beam identifier 6 (shown as crosshatched beams in combined second transmissions 1412).

In a third time 1415 and in a first sub-band, TRP 1405 transmitsbeamformed synchronization signals using active beams with beamidentifier 7 (shown as white beams in combined third transmissions1415), at the same time TRP 1405 transmits beamformed synchronizationsignals using the active beams rotated and with beam identifier 8 (shownas hatched beams in combined third subband transmissions 1415), and atthe same time TRP 1405 transmits beamformed synchronization signalsusing active beams rotated with beam identifier 9 (shown as crosshatched beams in combined third transmissions 1415). At a fourth time,TRP 1405 transmits beamformed broadcast signals as shown in combinedtransmissions 1416. Any of the previously described techniques fortransmitting beamformed broadcast signals, such as using TX diversity,different subbands, or a combination of different subbands and TXdiversity, etc., may be used.

In order for a UE to demodulate system information from beamformedbroadcast signals, the UE needs to be time (on a frame and subframebasis) and frequency synchronized with the TRP. As discussed previously,if the UE is able to determine the TRP beam index, the UE will also knowthe time offset between the received beamformed synchronization signaland the beamformed broadcast signals. Other benefits may be involvedwith the obtaining of the TRP beam index, as described below.

If the UE is able to determine good candidate beam directions from theTRP during the synchronization stage and feedback the information to theTRP (using dual connectivity with a legacy carrier, such as 3GPP LTE, orotherwise), subsequent processing or messaging to establish uplinksynchronization (i.e., when beamforming a RACH signal) or the assignmentof UE specific beamformed reference signals can be reduced. FIG. 15illustrates a diagram 1500 of messages exchanged and processingperformed by devices participating in synchronization. Devicesparticipating in synchronization include a TRP 1505, a UE 1510, and alegacy eNB 1515. A legacy connection 1520 exists between UE 1510 andlegacy eNB 1515. TRP 1505 transmits beamformed synchronization signalsand beamformed broadcast signals (events 1522 and 1523), and UE 1510receives the beamformed synchronization signals (event 1524) anddetermines time and frequency synchronization, as well as best beamidentity (block 1526). UE 1510 provides feedback of the best beamidentity, as well as optionally identifier of TRP 1505 to legacy eNB1515 (event 1528). Legacy eNB 1515 prepares TRP 1505 for beamformed RACH(event 1530), by providing the information received from UE 1510, forexample. UE 1510 transmits a beamformed RACH that is already pre-alignedto TRP 1505 (event 1532).

Furthermore, identifying and providing feedback about beam identities ofneighboring TRPs (derived from the beamformed synchronizationidentifiers of the neighboring TRPs) to the current TRP (or presentlyconnected TRP) can also accelerate neighbor cell reporting compared tosimply providing feedback about the beam-formed CSI-RS of theneighboring TRPs. This acceleration compared to using beam-formed CSI-RSis due to the fact, that beamformed CSI-RS indices of neighboring cellscan only be obtained once the CSI-RS configuration of the neighboringTRPs is known by the UE (by demodulating the beamformed broadcastsignals or otherwise, for example) before the beamformed CSI-RS can bedemodulated. In co-assigned patent application entitled “Beam Detection,Beam Tracking and Random Access in MM-Wave Small Cells in HeterogeneousNetwork,” application Ser. No. 14/791,112, filed Jul. 2, 2015, which ishereby incorporated herein by reference, techniques for feeding backbeam index information from beamformed CSI-RS (after synchronizing anddemodulating the beamformed broadcast signals) using dual connectivityto reduce processing are provided. In co-assigned patent applicationentitled “System and Method for Initial Attachment in a CommunicationsSystem Utilizing Beam-Formed Signals,” application Ser. No. 15/133,285,filed Apr. 20, 2016, which is hereby incorporated by reference,techniques for utilizing the boundary between different synchronizationsignals transmitted on wide beams to determine the timing of RACHtransmissions are provided.

Depending upon the system used, different sets of sequences may be usedto identify each of the beamformed synchronization signals. As anexample, if the communications system is using single carrier modulationwith frequency domain equalization (SC/FDE), Golay codes may be chosen,while if the communications system is using orthogonal frequencydivision multiplexing (OFDM), Zadoff-Chu (ZC) sequences may be chosen.Golay codes and ZC sequences are intended to be examples.

FIG. 16 illustrate a diagram 1600 of PSS and SSS in current generation3GPP LTE communications systems. As shown in FIG. 1600, the same PSS issent twice in every frame (every 10 slots) and indicates the physical(PHY) layer identity N_(ID) ⁽²⁾(0,1,2) based on the root of the ZCsequence root. The SSS sequence is an interleaved combination of twolength-31 sequences and is scrambled by a sequence derived from the PSS(the combination changes between slot 0 and slot 10. The SSS sequenceindicates the PHY layer cell identifier N_(ID) ⁽¹⁾, where cellidentifier=N_(ID) ^(cell)=3 N_(ID) ⁽¹⁾+N_(ID) ⁽²⁾.

Due to the current arrangement of the PSS/SSS in 3GPP LTE, the UE canobtain frame and slot timing, as well as obtain the cell identifier fromthe synchronization phase. The total required overhead is 6 RBs in 4slots of each frame (each frame has 120 slots). The exact overheaddepends upon the system bandwidth use, but may be as high as 3.33% whenthe system bandwidth is only 6 RBs.

In communications systems that use beamformed synchronization signals,such as those communications systems discussed herein, 2 sets of itemsmay be obtained:

a) Beam identifier (spatial synchronization), frequency and time (frameand slot) synchronization; or

b) Cell identifier, beam identifier (spatial synchronization), frequencyand time (frame and slot) synchronization.

It is clear that (b) would require a higher overhead compared to (a).Generic solutions for both (a) and (b) using the techniques describedherein are provided.

FIG. 17 illustrates a first example beamformed synchronization signalpayload and frame structure 1700 for spatial, frequency and timesynchronization. Beamformed synchronization signal frame structure 1700includes 10 subframes with 2 slots each subframe, including slot 0 1705of subframe 0 1707 and slot 10 1710 of subframe 5 1712. Slot 0 1705, aswell as slot 10 1710, comprises a plurality of symbols, some of whichare used to convey the beamformed synchronization signals. As anexample, symbol 1715 of slot 0 1705 includes RBs, such as RBs 1720,dedicated for transmitting the beamformed synchronization signals, aswell as other RBs, such as RBs 1722 and 1724, which are used by othersignals.

According to an embodiment, the sequences used in the second half of aframe structure, such as frame structure 1700, are complementaryversions of the sequences used in the first half of frame structure, sothe different pails of the frame can be identified and the subframe andframe timing can be established. In such a situation, each beamformedsynchronization signal symbol is transmitted twice in each frame. Searchcomplexity may be simplified and frame and slot timing is enabled. Asused herein, complementary sequences may include cyclically shiftedsequences, conjugated sequences, sequences with different roots, phaseshifts and so on.

FIG. 18 illustrates a second example beamformed synchronization signalpayload and frame structure 1800 for spatial, frequency and timesynchronization. Beamformed synchronization signal frame structure 1800includes 10 subframes with 2 slots in each subframe, including slot 01805 of subframe 0 1807 and slot 10 1810 of subframe 5 1812. Slot 01805, as well as slot 10 1810, comprises a plurality of symbols, some ofwhich are used to convey the beamformed synchronization signals. As anexample, symbol 1815 of slot 0 1805 includes RBs, such as RBs 1820 and1821, dedicated for transmitting different rotations of the beamformedsynchronization signals, as well as other RBs, such as RBs 1822 and1824, dedicated for other uses. As an example, RBs 1820 is used totransmit a first rotation of the beamformed synchronization signals andRBs 1821 is used to transmit a second rotation of the beamformedsynchronization signals.

According to an embodiment, the sequences used in the second half of aframe structure, such as frame structure 1800, are complementaryversions of the sequences used in the first half of frame structure sothe different parts of the frame can be identified and the subframe andframe timing can be established. The number of beamformedsynchronization signal symbols may be reduced by a factor of M/N asshown in FIG. 18, where M is the normal number of rotations needed and Nis the number of frequency subbands.

In order for a UE to determine the cell identifier or some kind ofidentifier of the TRP, additional information is needed. According to anexample embodiment, each active beam transmitting a beamformedsynchronization signal includes a beam identifier, a SSS, and a PSS.FIG. 19A illustrates a first example beamformed synchronization signalformat 1900. Beamformed synchronization signal format 1900 includes abeam identifier field 1905, a SSS field 1910, and a PSS field 1915. Beamidentifier field 1905 includes a sequence that is related to the beamidentifier associated with the active beam. SSS field 1910 includes asequence that is related to the SSS, such as a scrambling code. Thesequence is mapped to N_(ID) ⁽¹⁾ and the sequence used in slot 0 isdifferent from the sequence used in slot 10. PSS field 1915 includes asequence that is the same for all active beams from a single TRP. Thesequence is mapped to PHY layer identity N_(ID) ⁽²⁾.

According to an example embodiment, each active beam transmitting abeamformed synchronization signal includes a beam identifier and a SSScombined into one sequence, and a PSS. FIG. 19B illustrates a secondexample beamformed synchronization signal format 1950. Beamformedsynchronization signal format 1950 includes a SSS field 1955 and a PSSfield 1960. SSS field 1955 includes a sequence to the SSS, such as ascrambling code. The sequence is mapped to N_(ID) ⁽¹⁾ and the sequenceused in slot 0 is different from the sequence used in slot 10. Thesequence is also mapped to the beam identifier, such as a phase shift, acyclic shift, a code group mapping, and so on. PSS field 1960 includes asequence that is the same for all active beams from a single TRP. Thesequence is mapped to PHY layer identity N_(ID) ⁽²⁾. Because the exampleembodiments discussed herein reduce time overhead, both schemes in FIG.19A or 19B can be accommodated. If the techniques illustrated in FIG. 8are implemented (labeled as enhanced proposal 1 in FIG. 18), theimplementation of FIG. 19B would incur an overhead of 4 symbols in slots0 and 10 of a frame when the number of sub-bands is fixed to 2 (N=2),four beam are transmitted at the same time and a total 16 beamdirections are required. Other variations are possible.

In order for a UE to detect beamformed synchronization signals, the UEwill generally listen on all available receiver chains and will have abank of parallel correlators matched to known sequences. In a situationwhen the UE uses beamforming, e.g., with 90 degree half power bandwidth(HPBW) beams, the different receiver chains may listen to different beamdirections simultaneously. If the UE has 4 receive chains, the UE wouldbe able to listen in all directions (360 degrees) simultaneously. Thenumber of available receiver chains at the UE may be lower if the UE ismonitoring neighboring TRPs at the same time as it is receiving from theconnected TRP.

In order to enable the reception of interference free beamformedsynchronization signals for cell edge users, the beamformedsynchronization signals may be coordinated in time, frequency, andangular space, so that cell edge users only receive one beamformedsynchronization signal at a given frequency-time resource. Techniquesfor coordinating devices in the time, frequency, and angular space arediscussed in co-assigned patent application entitled “System and Methodfor beam-formed reference and control signals,” U.S. application Ser.No. 14/815,571, filed Jul. 31, 2015, which is hereby incorporated hereinby reference. In a situation when the UE is using beamforming, it mayonly be required for the TRPs to be coordinated when the TRPs are partof an ultra-dense network (UDN) or when each user's beam can receivesignals from different TRP simultaneously.

FIG. 20A illustrates a flow diagram of first example operations 2000occurring in a TRP transmitting beamformed control signals. Operations2000 may be indicative of operations occurring in a TRP of acommunications system as the TRP transmits beamformed control signals,including synchronization signals and broadcast signals.

Operations 2000 begin with the TRP determining a set of spatiallyseparated transmission beams (block 2005). The set of spatiallyseparated transmission beams may be specified by a technical standard oran operator of the communications system. In such a situation, the setof spatially separated transmission beams may be stored in memory of theTRP. Alternatively, the TRP may retrieve the set of spatially separatedtransmission beams from a server (local or remote) or from some otherdevice in the communications system The set of spatially separatedtransmission beams may be coordinated with sets of spatially separatedtransmission beams of neighboring TRPs. Alternatively, the TRP mayselect the set of spatially separated transmission beams. The selectionof the set of spatially separated transmission beams may be made inaccordance with factors such as a number of available transmissionbeams, a number of available frequency subbands, beamformingcapabilities of the TRP, receive capabilities of the UEs, mobility ofthe UEs, tolerable communications overhead, tolerable synchronizationlatency, and so on.

The TRP beamforms a synchronization signal in accordance with the set ofspatially separated transmission beams (block 2010). If multiplesubbands are used, the TRP may beamform the synchronization signal inaccordance with the set of spatially separated transmission beams foreach of the subbands. The TRP transmits the beamformed synchronizationsignals (block 2015). The transmission of the beamformed synchronizationsignals may occur in a single band or in multiple subbands, depending onthe configuration of the communications system. The TRP performs a checkto determine if a synchronization cycle is complete (block 2020). As anexample, the synchronization cycle is complete if the TRP hastransmitted beamformed synchronization signals on all availabletransmission beams. Alternatively, the synchronization cycle may beshorter than what is needed to allow the TRP to transmit beamformedsynchronization signals on all available transmission beams. An exampleof such synchronization cycles are shown in FIGS. 6A-6F, where a fullsynchronization cycle would comprise 4 rotations of the set of spatiallyseparated transmission beams but the synchronization cycle ispartitioned into two separate synchronization cycles of 2 rotations ofthe set of spatially separated transmission beams each. If thesynchronization cycle is not complete, the TRP rotates the set ofspatially separated transmission beams (block 2025). The rotation of theset of spatially separated transmission beams is specified during thedetermining of the set of spatially separated transmission beams andensures that the TRP transmits the beamformed synchronization signals onall available transmission beams by the time the synchronization cycle(or synchronization cycles in the situation where the synchronizationcycle is shorter than what is needed to allow the TRP to transmitbeamformed synchronization signals on all available transmission beams)is complete. The TRP returns to block 2010 to beamform thesynchronization signal in accordance with the rotated set of spatiallyseparated transmission beams.

If the synchronization cycle is complete, the TRP beamforms a broadcastsignal (block 2030) and transmits the beamformed broadcast signals(block 2035). Any of the previously described techniques fortransmitting beamformed broadcast signals, such as using TX diversity,different subbands, or a combination of different subbands and TXdiversity, etc., may be used. If the synchronization cycle waspartitioned into multiple synchronization cycles, the TRP returns toblock 2010 to start another synchronization cycle. The TRP performs acheck to determine if the synchronizing cycle is complete (block 2040).If the synchronizing cycle is not complete, the TRP changes the set ofspatially separated transmission beams (which may be as simple asapplying a rotation to the set of spatially separated transmissionbeams) and returns to block 2010 to continue transmission of beamformedsynchronization signals. For discussion purposes, consider thesynchronization cycles as shown in FIGS. 6A-6F; In such a situation, afirst synchronization cycle comprises transmissions on 2 rotations ofthe set of spatially separated transmission beams as shown in FIGS. 6Aand 6B and a second synchronization cycle comprises transmissions on 2rotations of the set of spatially separated transmission beams as shownin FIGS. 6D and 6E, while the synchronizing cycle comprises thetransmissions as shown in FIGS. 6A-6F. Once the synchronizing cycle iscomplete, the TRP may prepare for RACH reception from a UE (block 2040).

FIG. 20B illustrates a flow diagram of second example operations 2050occurring in a TRP transmitting beamformed signals. Operations 2050 maybe indicative of operations occurring in a TRP of a communicationssystem as the TRP transmits beamformed signals, includingsynchronization signals. It is noted that operations 2050 may beapplicable in situations where an entity other than the TRP transmitsbroadcast signals, such as in a heterogeneous deployment or a dualconnectivity deployment, transmits broadcast signals and the TRPtransmits beamformed signals (including synchronization signals).

Operations 2050 begin with the TRP determining a set of spatiallyseparated transmission beams (block 2055). The set of spatiallyseparated transmission beams may be specified by a technical standard oran operator of the communications system. In such a situation, the setof spatially separated transmission beams may be stored in memory of theTRP. Alternatively, the TRP may retrieve the set of spatially separatedtransmission beams from a server (local or remote) or from some otherdevice in the communications system The set of spatially separatedtransmission beams may be coordinated with sets of spatially separatedtransmission beams of neighboring TRPs. Alternatively, the TRP mayselect the set of spatially separated transmission beams. The selectionof the set of spatially separated transmission beams may be made inaccordance with factors such as a number of available transmissionbeams, a number of available frequency subbands, beamformingcapabilities of the TRP, receive capabilities of the UEs, mobility ofthe UEs, tolerable communications overhead, tolerable synchronizationlatency, and so on.

The TRP beamforms a synchronization signal in accordance with the set ofspatially separated transmission beams (block 2060). If multiplesubbands are used, the TRP may beamform the synchronization signal inaccordance with the set of spatially separated transmission beams foreach of the subbands. The TRP transmits the beamformed synchronizationsignals (block 2065). The transmission of the beamformed synchronizationsignals may occur in a single band or in multiple subbands, depending onthe configuration of the communications system. The TRP performs a checkto determine if a synchronization cycle is complete (block 2070). As anexample, the synchronization cycle is complete if the TRP hastransmitted beamformed synchronization signals on all availabletransmission beams. Alternatively, the synchronization cycle may be lessthan what is needed to allow the TRP to transmit beamformedsynchronization signals on all available transmission beams. An exampleof such synchronization cycles are shown in FIGS. 6A-6F, where a fullsynchronization cycle would comprise 4 rotations of the set of spatiallyseparated transmission beams but the synchronization cycle ispartitioned into two separate synchronization cycles of 2 rotations ofthe set of spatially separated transmission beams each. If thesynchronization cycle is not complete, the TRP rotates the set ofspatially separated transmission beams (block 2075). The rotation of theset of spatially separated transmission beams is specified during thedetermining of the set of spatially separated transmission beams andensures that the TRP transmits the beamformed synchronization signals onall available transmission beams by the time the synchronization cycleis complete. The TRP returns to block 2060 to beamform thesynchronization signal in accordance with the rotated set of spatiallyseparated transmission beams. If the synchronization cycle is complete,the TRP performs a check to determine if the synchronizing cycle iscomplete (block 2080). If the synchronizing cycle is not complete, theTRP changes the set of spatially separated transmission beams (which maybe as simple as applying a rotation to the set of spatially separatedtransmission beams) (block 2085) and returns to block 2060 to continuetransmission of beamformed synchronization signals. Once thesynchronizing cycle is complete, the TRP may prepare for RACH receptionfrom a UE (block 2090).

FIG. 21 illustrates a flow diagram of example operations 2100 occurringin a UE performing synchronization. Operations 2100 may be indicative ofoperations occurring in a UE of a communications system as the UEperforms synchronization utilizing beamformed control signals, includingsynchronization signals and broadcast signals.

Operations 2100 begins with the UE performing a check to determine if abeamformed synchronization signal has been received (block 2105). If abeamformed synchronization signal has been received, the UE determinesthe beam identifier of the received beamformed synchronization signal(block 2110). The UE performs a check to determine if thesynchronization cycle is complete (block 2115). If the synchronizationcycle is not complete, the UE returns to block 2105 to potentiallyreceive additional beamformed synchronization signals. The UE may notreceive any other beamformed synchronization signals depending on thelocation of the UE with respect to the TRP transmitting the beamformedsynchronization signals.

If the synchronization cycle is complete, the UE determines a beam indexof a transmission beam oriented towards the UE (block 2120). Thedetermination of the beam index is made using the one or more beamidentities of the one or more beamformed synchronization signalsreceived by the UE, as determined in block 2110. The UE receives abroadcast signal (block 2125). The broadcast signal may be a beamformedbroadcast signal from the TRP, such as described in FIG. 20A.Alternatively, the broadcast signal may be received from a legacy eNB ina dual connectivity deployment. Although the discussion focuses on thebroadcast signal being received once the synchronization cycle iscomplete, the broadcast signal may be received at any time, such asbefore the synchronization cycle, during the synchronization cycle, orafter the synchronization cycle. It is noted that if the synchronizationcycle is partitioned into multiple synchronization cycles, such as shownin FIGS. 6A-6F, the UE is not ensured of receiving either a beamformedsynchronization signal or a beamformed broadcast signal in any givensynchronization cycle. However, the UE is ensured of receiving at leastone beamformed synchronization signal and one broadcast signal over theentirety of the synchronizing cycle.

The UE optionally feeds back the beam index (block 2130). In a dualconnectivity deployment, the beam index may be fedback to a legacy eNBthat is serving the UE. The UE performs a RACH procedure with the TRP(block 2135). The TRP can use this beam index information to prepare theTRP to receive on the correct beam for the RACH procedure. UE uses thebeam index for timing information and to know when to transmit the RACH.The UE may beamform the RACH transmission in accordance with the beamindex.

FIG. 22 illustrates a block diagram of an embodiment processing system2200 for performing methods described herein, which may be installed ina host device. As shown, the processing system 2200 includes a processor2204, a memory 2206, and interfaces 2210-2214, which may (or may not) bearranged as shown in FIG. 22. The processor 2204 may be any component orcollection of components adapted to perform computations and/or otherprocessing related tasks, and the memory 2206 may be any component orcollection of components adapted to store programming and/orinstructions for execution by the processor 2204. In an embodiment, thememory 2206 includes a non-transitory computer readable medium. Theinterfaces 2210, 2212, 2214 may be any component or collection ofcomponents that allow the processing system 2200 to communicate withother devices/components and/or a user. For example, one or more of theinterfaces 2210, 2212, 2214 may be adapted to communicate data, control,or management messages from the processor 2204 to applications installedon the host device and/or a remote device. As another example, one ormore of the interfaces 2210, 2212, 2214 may be adapted to allow a useror user device (e.g., personal computer (PC), etc.) tointeract/communicate with the processing system 2200. The processingsystem 2200 may include additional components not depicted in FIG. 22,such as long term storage (e.g., non-volatile memory, etc.).

In some embodiments, the processing system 2200 is included in a networkdevice that is accessing, or part otherwise of, a telecommunicationsnetwork. In one example, the processing system 2200 is in a network-sidedevice in a wireless or wireline telecommunications network, such as abase station, a relay station, a scheduler, a controller, a gateway, arouter, an applications server, or any other device in thetelecommunications network. In other embodiments, the processing system2200 is in a user-side device accessing a wireless or wirelinetelecommunications network, such as a mobile station, a user equipment(UE), a personal computer (PC), a tablet, a wearable communicationsdevice (e.g., a smartwatch, etc.), or any other device adapted to accessa telecommunications network.

In some embodiments, one or more of the interfaces 2210, 2212, 2214connects the processing system 2200 to a transceiver adapted to transmitand receive signaling over the telecommunications network. FIG. 23illustrates a block diagram of a transceiver 2300 adapted to transmitand receive signaling over a telecommunications network. The transceiver2300 may be installed in a host device. As shown, the transceiver 2300comprises a network-side interface 2302, a coupler 2304, a transmitter2306, a receiver 2308, a signal processor 2310, and a device-sideinterface 2312. It is noted that coupler 2304 is typically present in atransceiver of a frequency division duplexed (FDD) communicationssystem. In a time division duplexed (TDD) communications system, aswitch would be present instead. The network-side interface 2302 mayinclude any component or collection of components adapted to transmit orreceive signaling over a wireless or wireline telecommunicationsnetwork. The coupler 2304 may include any component or collection ofcomponents adapted to facilitate bi-directional communication over thenetwork-side interface 2302. The transmitter 2306 may include anycomponent or collection of components (e.g., up-converter, poweramplifier, etc.) adapted to convert a baseband signal into a modulatedcarrier signal suitable for transmission over the network-side interface2302. The receiver 2308 may include any component or collection ofcomponents (e.g., down-converter, low noise amplifier, etc.) adapted toconvert a carrier signal received over the network-side interface 2302into a baseband signal. The signal processor 2310 may include anycomponent or collection of components adapted to convert a basebandsignal into a data signal suitable for communication over thedevice-side interface(s) 2312, or vice-versa. The device-sideinterface(s) 2312 may include any component or collection of componentsadapted to communicate data-signals between the signal processor 2310and components within the host device (e.g., the processing system 2200,local area network (LAN) ports, etc.).

The transceiver 2300 may transmit and receive signaling over any type ofcommunications medium. In some embodiments, the transceiver 2300transmits and receives signaling over a wireless medium. For example,the transceiver 2300 may be a wireless transceiver adapted tocommunicate in accordance with a wireless telecommunications protocol,such as a cellular protocol (e.g., long-term evolution (LTE), etc.), awireless local area network (WLAN) protocol (e.g., Wi-Fi, etc.), or anyother type of wireless protocol (e.g., Bluetooth, near fieldcommunication (NFC), etc.). In such embodiments, the network-sideinterface 2302 comprises one or more antenna/radiating elements. Forexample, the network-side interface 2302 may include a single antenna,multiple separate antennas, or a multi-antenna array configured formulti-layer communication, e.g., single input multiple output (SIMO),multiple input single output (MISO), multiple input multiple output(MIMO), etc. In other embodiments, the transceiver 2300 transmits andreceives signaling over a wireline medium, e.g., twisted-pair cable,coaxial cable, optical fiber, etc. Specific processing systems and/ortransceivers may utilize all of the components shown, or only a subsetof the components, and levels of integration may vary from device todevice.

It should be appreciated that one or more steps of the embodimentmethods provided herein may be performed by corresponding units ormodules. For example, a signal may be transmitted by a transmitting unitor a transmitting module. A signal may be received by a receiving unitor a receiving module. A signal may be processed by a processing unit ora processing module. Other steps may be performed by a beamformingunit/module, a determining unit/module, a rotating unit/module, and/or arepeating unit/module. The respective units/modules may be hardware,software, or a combination thereof. For instance, one or more of theunits/modules may be an integrated circuit, such as field programmablegate arrays (FPGAs) or application-specific integrated circuits (ASICs).

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims.

What is claimed is:
 1. A method for transmitting beamformed signals, themethod comprising: beamforming, by a transmit-receive point (TRP), asynchronization signal in accordance with a first set of spatiallyseparated transmission beams, thereby producing first beamformedsynchronization signals; beamforming, by the TRP, a broadcast signal inaccordance with the first set of spatially separated transmission beams,thereby producing first beamformed broadcast signals; transmitting, bythe TRP, the first beamformed synchronization signals; transmitting, bythe TRP, the first beamformed broadcast signals; determining, by theTRP, if a first cycle is complete; and based on the first cycle notbeing complete, rotating, by the TRP, the first set of spatiallyseparated transmission beams, and repeating, by the TRP, thebeamformings, the transmittings, and the determining until the firstcycle is complete.
 2. The method of claim 1, wherein the firstbeamformed synchronization and broadcast signals oriented in differentdirections are transmitted in different subbands.
 3. The method of claim1, wherein the first beamformed broadcast signals oriented in differentdirections are transmitted with transmit diversity.
 4. The method ofclaim 1, wherein the transmitting the first beamformed synchronizationand broadcast signals comprises transmitting the first beamformedsynchronization and broadcast signals for one of a symbol time, a timeslot duration, or a subframe duration.
 5. The method of claim 1, whereinthe transmitting the first beamformed synchronization signals comprisestransmitting the first beamformed synchronization signals using onesequence for all transmission beams in the first set of spatiallyseparated transmission beams.
 6. The method of claim 1, wherein thetransmitting the first beamformed synchronization signals comprisestransmitting the first beamformed synchronization signals using adifferent sequence for each transmission beam in the first set ofspatially separated transmission beams.
 7. A transmit-receive point(TRP) adapted to transmit beamformed control signals, the TRPcomprising: a non-transitory memory storage comprising instructions; anda processor in communication with the non-transitory memory storage,wherein the processor executes the instructions to: beamform asynchronization signal in accordance with a first set of spatiallyseparated transmission beams, thereby producing first beamformedsynchronization signals, beamform a broadcast signal in accordance withthe first set of spatially separated transmission beams forsynchronization, thereby producing first beamformed broadcast signals,transmit the first beamformed synchronization signals, transmit thefirst beamformed broadcast signals, determine if a first cycle iscomplete, and based on the first cycle being not complete, rotate thefirst set of spatially separated transmission beams, and repeat thebeamformings, the transmittings, and the determining until the firstcycle is complete.
 8. The TRP of claim 7, wherein the processor executesthe instructions to: beamform the synchronization signal in accordancewith a second set of spatially separated transmission beams, therebyproducing second beamformed synchronization signals, transmit the secondbeamformed synchronization signals; determine if a secondsynchronization cycle is complete; and based on the secondsynchronization cycle not being complete, rotate the second set ofspatially separated transmission beams, and repeat beamforming thesynchronization signal in accordance with the second set of spatiallyseparated transmission beams, transmitting the second beamformedsynchronization signals, and determining if the second synchronizationcycle is complete until the second synchronization cycle is complete. 9.The TRP of claim 7, wherein the processor executes the instructions totransmit the first beamformed synchronization and broadcast signals forone of a symbol time, a time slot duration, or a subframe duration. 10.The TRP of claim 7, wherein the first beamformed synchronization andbroadcast signals oriented in different directions are transmitted indifferent subbands.
 11. The TRP of claim 7, wherein the first beamformedbroadcast signals oriented in different directions are transmitted withtransmit diversity.
 12. The TRP of claim 7, wherein the processorexecutes the instructions to transmit the first beamformedsynchronization signals comprises the processor executes theinstructions to transmit the first beamformed synchronization signalsusing one sequence for all transmission beams in the first set ofspatially separated transmission beams.
 13. The TRP of claim 7, whereinthe processor executes the instructions to transmit the first beamformedsynchronization signals comprises the processor executes theinstructions to transmit the first beamformed synchronization signalsusing a different sequence for each transmission beam in the first setof spatially separated transmission beams.